The “DEFCON” (defense condition) system is a threat-display, now, but during the early cold war it was important.
In fact, it turns out, NORAD and the US Air Force’s strike forces were not correctly deployed, and were susceptible to a first strike. That doesn’t mean, as we’d expect it would, that Curtis Le May would get fired from his job – oh, no, it meant that Curtis Le May was ready to launch a civilization-killing attack on his own recognizance, as soon as it looked like a Soviet attack was coming. Talk about MAD: Le May’s stated plan was that if he got sufficiently worried, the US would launch a first strike. Meanwhile, the US talked a good game about how the nukes were under political control, and a “deranged general” scenario could not happen. We don’t need to dwell on that, because we survived that particular speed-bump – but it’s illustrative of the way that building and having weapons of mass destruction inevitably sucks a government into lying to its own people – you can’t build things like that without trying to cover up the insane crime you’re committing.
Anyhow, the US has its DEFCON, which no longer means the bombers are in the air, loaded with nukes, and flying a big circle up in the arctic. It probably means that the commanders of the ballistic missile subs, who have a great deal of leeway over launch decisions and targeting, are cruising toward good launching positions, and (probably) diving deep and taking evasive courses to throw off any satellites that may be tracking them. The US hasn’t gone to DEFCON 3 very often: 9/11, the Cuban Missile Crisis, the Matsu/Quemoy incident, perhaps a few other things we don’t know about. It doesn’t change things much, except there’s one significant bit: if a missile launch commander is at DEFCON 2 and gets a launch order, they are much more likely to carry it out than if they got it on a sunny day when they weren’t on alert. It’s a mistake magnifier.